TM 9-1005-245-14 with all the Army's weapon mounts dated up to 1973 is what you are looking for. Getting it is tricky, it's not a widely published item so I've scanned any pages they had about it...only 3. I skimmed through mine and it doesn't list the vehicle applications for the "M68 series mounts" and only lists one ring: M68/M68E1 and is clearly for armored vehicles. Thicker, rear bar (for holding onto while climbing on top of a tank), no support legs only short ones, part of a bigger setup, and no installation instructions. Basically not a unit level install and will not fit a deuce. Best thing to do is take pictures and post them here so we can check against other sources to verify exactly what it is. If anything save yourself some work and trade it to someone for an M66 gunring. The m66 ring is heavy for a deuce to begin with..cant imagine an even heavier one on that cab.
